device tree files should be ./your_workspase_project/tmp/work-shared/ccimx6ulsbc/kernel-source/arch/arm/boot/dts/
Here is what I do to change device tree and re-compile:
source dey-setup-environment
bitbake -c devshell virtual/kernel
—this will start a development shell------
vi arch/arm/boot/dts//imx6qp-ccimx6qpsbc.dtsi
exit
----This will exit the development shell
Above is optional as you can simply edit files directly in ./your_workspase_project/tmp/work-shared/ccimx6ulsbc/kernel-source/arch/arm/boot/dts/
bitbake -c compile -f u-boot-dey
bitbake -c compile -f linux-dey
bitbake -c deploy linux-dey
bitbake dey-image-qt